Luna
In spite of fertility problems, Orions still manage to keep their numbers up. That means that overall, infertile and hanyo Orions still fit into the survival of the species. That’s why those traits haven’t bred out over the centuries.

The Y chromosome is more readily damaged by radiation, but it also happens to the X chromosome, too. So there must be some kind of check on genetic stability, either in your own makeup, or something done in the gestation tanks. Males with the most severe damage don’t ever make it to a fetal stage. Other males become hanyo instead. Only the healthiest, most genetically stable Orions have children. In litters. Non-breeders still contribute by caring for the children of friends and family members.

The mutation that allows most modern Earth humans to drink milk probably goes all the way back to livestock domestication. Around 10,000 years ago, or more. We know Orions are an off-shoot of humanity, which it would seem, goes back to before the lactose adaptation.

I think there was something about the people that became Orions dying off due to starvation and competition. Orions need a high protein diet, but not like Neanderthals that were almost obligate carnivores. I’d have to say this would have been in the early part to middle of the last ice age.

We know that Neanderthals died off during that time, but they were really robust. Orions are not. Denisovans, we don’t know so much about. Especially since they practically vanished from the fossil record. We know that there was infrequent interbreeding between Neanderthals, Denisovan, and Modern Humans. It’s been suggested that Nepalese and Tibetans, who are adapted to high altitude living and higher solar radiation tolerance, may have Denisovan genes.

This would explain the Orion’s limited creativity. Modern human’s creativity and communication skills are centered in the portions of the brain most influenced by Neanderthal DNA from when early humans migrated into Neanderthal territory and interbred with them.